Stretched vortices as a basis for subgrid-scale modeling

Dale Pullin, Graduate Aeronautical Laboratories, California Institute of Technology, USA

This lecture will describe a framework for structure-based, subgrid-scale (SGS) modeling for the large-eddy simulation of turbulence using stretched vortices. The starting point is the scale-separation into resolved-scales, that are simulated numerically, and subgrid scales that are modeled. The most general subgrid, vortex-like element consists of a columnar vortex structure rotating, tilting, stretching and evolving within a background spatially linear velocity field that represents the forcing of the large scales. This reduces to an ensemble of three-component, two-dimensional Navier-Stokes problems, each coupled to the local resolved-scale motion at the cutoff. Analytical simplification of this ansatz using the stretched-spiral vortex will then be shown to lead to a tractable and efficient subgrid-scale modeling approach in which coupling constants are evaluated dynamically using velocity and/or scalar structure functions matched to the local resolved-scale field. The final result is the "stretched-vortex subgrid-scale" model.